1. Field of the Invention
The present invention relates to an optical pickup actuator, and more particularly, to an optical pickup actuator having a bobbin having first opposite sides and second opposite sides, focus coils, track coils, and tilt coils disposed on the first opposite sides of the bobbin, to drive the bobbin in a focus direction, a track direction, and a tilt direction, and a support disposed on the second opposite sides of the bobbin to support the bobbin on the optical pickup actuator.
2. Description of the Related Art
In general, optical pickup actuators have been used in optical recording/reproducing devices and control an optical pickup to move in a non-contact way in a radial direction of a recording medium (disc) mounted on a turntable to record/reproduce data on/from the optical medium.
The optical pickup includes an objective lens condensing light emitted from a light source to form a light spot on the optical medium and an actuator controlling the objective lens in a track direction, a focus direction, and a tilt direction to accurately position the light spot on the optical medium.
The optical pickup actuator includes a 2-axis driving actuator driving the objective lens in the track and focus directions. However, as the number of numeral apertures of the objective lens increases for high density recording and a wavelength of a laser beam is reduced, a tilt margin of the optical pickup actuator decreases. To compensate for this, a 3-axis or 4-axis driving actuator driving in the tilt direction as well as the track and focus directions is required. The 3-axis driving actuator allows the objective lens to move in the focus, track, and tilt radial directions. The 4-axis actuator allows the objective lens to move in the focus, track, tilt radial, and tilt tangential directions. In FIG. 1, the focus, track, tilt radial, and tilt tangential directions are represented as L-L′, M-M′, N, and O, respectively.
Referring to FIG. 1, a conventional optical pickup actuator includes a base 100, a holder 103 fixed on the base 100, a bobbin 107 having an objective lens 105, wires 109 connecting the holder 103 to the bobbin 107, and a magnetic driver (not shown) driving the bobbin 107 in the track and focus directions or the tilt direction.
As shown in FIGS. 1, 2A and 2B, the magnetic driver includes focus coils 110 and tilt coils 112 both forming two pairs, track coils 115, first magnets 117, and second magnets 119. The focus coils 110 and the tilt coils 112 are disposed on first opposite sides 107a of the bobbin 107. The track coils 115 are disposed on second opposite sides 107b of the bobbin 107. The first magnets 117 and the second magnets 119 are installed on the base 100 to be spaced-apart from the focus coils 110, the tilt coils 112, and the track coils 115. Outer yokes 118 and 120 are installed on the base 100 and support corresponding ones of the first magnets 117 and the second magnets 119. Inner yokes 122 are installed on the base 100 to correspond to the first magnets 117 to guide the bobbin 107. The outer and inner yokes 118, 120, and 122 induce a magnetic field created by the first and second magnets 117 and 119 in a desired direction.
The wires 109 are soldered on two second opposite sides of the bobbin 107 and coupled to the holder 103 to electrically connect the magnetic driver to a circuit unit (not shown), which supplies current to the magnetic driver having the focus coils 110, the tilt coils 112, and the track coils 115.
FIG. 2A schematically shows a polarity of the first magnets 117 and directions of the current to observe a relationship of interaction forces between the focus and tilt coils 110 and 112, and the first magnets 117. Here, the focus coils 110 on two first opposite sides 107a of the bobbin 107 receive a focusing force Ff according to Fleming's left-hand law so that the bobbin 107 moves in the focus direction L. The focus coils 110 receive an opposite focusing force in an opposite focus direction L′ if the direction of the supplied current is changed.
The tilt coils 112 form pairs with the focus coils 110 on the first opposite sides 107a of the bobbin 107 to interact with the first magnets 117. Here, if the tilt coils 112 on the first opposite sides 107a of the bobbin 107 are supplied with the current having the same intensity and opposite direction as those of the focus coils 110, the tilt coils 112 receive one of tilting forces Fti with opposite directions. Thus, the bobbin 107 is driven in the tilt direction and particularly in the radial tilt direction N.
FIG. 2B schematically shows the polarity of the second magnets 117 and the directions of the current to observe the relationship of the interaction forces between the track coils 115 and the second magnets 117. The directions and magnitudes of the interaction forces between magnets and coils are determined based on Fleming's left-hand law. Thus, the track coils 115 on the second opposite sides 107b of the bobbin 107 receive a tracking force Ft in the track direction due to the second magnets 119 so that the bobbin 107 moves in the track direction M. Here, if the direction of the supplied current is changed, the track coils 115 receive an opposite tracking force in the opposite track direction M′.
The wires 109 of the optical pickup actuator generally include six wires driving the bobbin 107 in the focus, track, and tilt directions. The 4-axis driving actuator may require more wires. However, since the optical pickup actuator is very small in size, there is not enough space to install the wires 109 on the bobbin 107 if the four first and second opposite sides 17a, 17b of the bobbin 107 are used to install the focus coils, track coils, and tilt coils. Also, if the number of wires 109 increases, it is difficult to adhere the wires to corresponding sides 17a, 17b of the bobbin 107 in such a narrow space. As a result, the poor adhesion of the wires 109 on the bobbin 107 increases.
Moreover, if the four first and second opposite sides 17a, 17b of the bobbin 107 are all used to be mounted with the focus, tilt, and track coils 110, 112, and 115, a connection between the focus, tilt, and track coils 110,112, and 115 becomes complicated. Also, since each of the focus, tilt, and track coils 110, 112, and 115 requires a magnet, the number of parts increases, and thus, productivity of the optical pick actuator decreases. Also, since the first magnets 117 for the focus coils 110 disposed on the first opposite sides of the bobbin 107 may interfere with a spindle motor (not shown) rotating the optical medium, the control of the spindle motor can be obstructed.